A tire for a construction vehicle is mounted on a heavy dump truck, etc. to be utilized at a large scale civil construction site or an ore mine is subjected to harsh working conditions of a heavy load on rough ground surfaces. Since a tire for a construction vehicle destined for running over rough surfaces receives a strong force from a road surface as well as a heavy load by nature, high tensile strength (breaking force) is required for a steel cord to be used for respective reinforcing layers, such as a carcass and a belt.
Consequently, for such reinforcing layers, a steel cord with a so-called multi-twisted structure, such as a 7×(3+9) structure and a 7×(3+9+15) structure (for example, Patent Documents 1 and 2) and a (3+8+13+18) 4-layer-twisted structure (Patent Documents 3 and 4) in which a plurality of sheath strands formed by twisting a plurality of wires are twisted around a core strand formed by twisting a plurality of wires has been used broadly.
Further, a tire for a construction vehicle has high risks of being damaged as the result of incurring the high load on the rough ground surface, and such countermeasures have been taken, as use of a large diameter cord as a reinforcing cord, and use of a so-called high tensile strength steel to increase the tensile breaking force per unit area of the cord, so as to increase the tensile breaking strength in the axial direction of the cord.